Treating metal filaments.



G. T. FULLER. TREATING MTAL PILAMENTS.

APPLIOATION FILED AUG. 24, 1907.

Patented July 27, 1909.

ATTN:

NVENTUR EARLTFULLER, BVM

WITNBSEEB UNTTE STAT naar fr uric.

CARL T. FULLER, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK. l

TREATING- METAL FILAMNTS. n

specification of Letters Patent.

Patented July 27, 1909.

Application filed August 24, 1907. Serial No. 390,048.

To all whom itin/Lay concern.:

Be 1t known that I, Gann T. FULLER, a citizen of the Unit-ed States, residing at Schenectady, county of Schenectady, State a reducible compound of a refractory metal is mixedwith a binder and shaped into wires'or other forms, and then tired in a reducing atmosphere to effect reduction of the oXid and complete shrinkage and sintering of the refractory residue, thereby producing conductors which are strong and homogeneous and are permanent in electrical conductivity.

My process' is applicable to the product-ion of conductors ofv various refractory metals and materials, such for instance as tungsten, molybdenum, boron, zirconium, tantalum, titanium, graphite, or compounds or alloys of any of these, or of other materials of the same general refractory nature.

In order that my invention may be easily applied, I have hereinafter described the process as applied to the production-of tungsten conductors, but this specific embodiment is to be regarded as only typical and as showing but one of numerous applications. As the rcducible compound of tungsten with which the process is begun, I prefer to use the yellow or trioxid of tungsten. This material should be in a very finely divided condition and should be pure. As a binding material for this yellow oXd, I prefer to use a starch paste compounded from 100 c. c. water and 25 grams cornstarch cooked until the wateris driven off suiiicicntly to leave a sticky paste containing 23%` starch, by weight. i

In mixing the starch paste with the yellow oXid, I start with 25 grams paste and add as much ox'id as the paste will take up, yielding a sticky and workable mass. ,lhe exact quantity of oxid taken up depends on the fineness of the oXid 'but should ordinarily be readily squirted through a die to produce threads, bars, plates, and similar shapes.

The next step in my process consists in the reduction in a furnace of the tungsten trioxid by'means of hydrogen or other gaseous reducing agent. A furnace suitable for this operation is shown in the accompanying drawing, in which- Figure 1 is a sectional elevation of the furnace, partly diagrammatic, and Fig. 2 is a .perspective'view of the shuttle or boat in which the filaments or threads are inclosed during the treatment.

The furnace illustrated in Fig. 1 comprises a graphite heater tube l supplied with current through suitable terminals 2 and 3, and inclosed in a protective coating l of coke or other refractory material. Nithin this tube, a second tube 5 may bel inserted and withdrawn. rIhis second tube is continuously supplied with hydrogen through a' rubber tube 6 and serves as a receptacle for the boats or shuttles 7 containing the material to be treated. I prefer that tube 5 should have a small bore at the end connecting with the rubber tube 6 and should have an enlargement at the end containing the boat 7 The refractory boat consists of a trough-shapedI member having side walls 8 and a central web 9 and having a lining of refraetoryrmaterial 10 consisting of rutile or of other materials hereinafter mentioned. A post 11 of rutile is mounted at one end of the boat to serve as an anchoring device for the filaments under treatment. To effect reduction 'of the squirted threads of IVO3 I withdraw the tube 5 from the furnace, arrange the threads in vbundles on the rutile packing 10 of boats 7, introduce these boats into the tube and return the tube 5 to its position within the heated tube 1, maintaining during this time a stream of hydrogen through the tube 5. As the tungsten trioxid heats up in the furnace it is attacked Aby the carbon of the binding means and is in part reduced thereby. Itis further reduced by the current 'of hydrogen circulating through thetube. Complete reduction may require only a' few minutes and yields pure tungsten threads or wires relatively fragile, and unshrunk, and therefore unsuited for use in lamps without subsequent treatment to give thempermancnce. The next step, o1' what may possibly be considered as a continuation of the previous step, consists in continuing the heat treatment, that is, firing to sucha high temperature and for such a length of time as will completely sinter and shr1nk the tungsten wires and render them. suitable for i mounting in lamps without any subsequent treatment whatever. These baking and firing operations require not more than about eight minutes at a temperature of about 147 5 to 1550 degrees C.

Now I have found that something more than rough heat treatment to the temperatures above mentioned, is necessary to yield a product having sufficient stability or electrical permanence to permit commercial use lin lamps without subsequent individual defective by reason of the presence of carbon.-

I have found how to overcome all these difficulties and I will hereinafter specify the precautions which I consider advisable. First of all, the filaments or threads should be completely reduced; that is, should contain no residue of unreduced oxid of tungsten. By using the starch binder above described and plenty of hydrogen in the inner tube 5, no serious difficulty will be encountered along this line. I find, however, that the hydrogen supplied to tube 5 may be advantageously returned on the outside of that tube and burned at the end of the heater tube "5. This result is easily effected by closing the heater tube with a plug 12. The next factor which in my oplnion influences the shrinkage is the presence or absence of carbon during the firing or high heat treatment. By this I do not mean carbon from the binder, as that all comes out at an early stage in the treatment, but I do mean carbon from the heating members of the furnace. This can be guarded against by the use of proper material for the boat or shuttle illustrated in Fig. 2 of the drawing. In general, I prefer that .the boat shall consist of or comprise a material having a high affinity for carbon, or at least having as great a tendency to absorb carbon asV do the filaments under treatment. Such a body acts as an absorbing shield to take up any carbon vapor given off by the furnace tube. l

Off the various materials usedby me in constructing the boats, I havefobtained best results witha carbon boat having apacking lating through the' tube.

of rutile TiO'2 the materials being arranged as shown in Fig. 2 of the drawing. I have also successfully used carbon boats lined with powdered tungsten. Either rutile or powdered tungsten serves, by virtue of itshigh afiinity for carbon, to protect the filaments from Whatever carbon vapor may be circu These materials also possess the very important requisite of not stickin to the filaments or combining therewith, 1n this respect being similar Yto powdered silica which I have successfully used, and being, in my opinion, far superior to oXids of the earth metals, such vas thorium, magnesium, cerium, etc. By the use of materials which do not become sticky, the filaments are free to move longitudinally in the boats and are free to undergo complete shrinkage. When'treated as above described, they do undergo this shrinkage, and they attain an electrical resistance which remains substantially constant throughout their normal life as filamentsin lamps. This resistance is directly comparable with the resistance of filaments shrunk or sintered 90 individually with current in a treating bottle.

My furnace method of firing and shrinking has great commercial advantage in that it permits simultaneous treatment of dozens or even hundreds of filaments, and furthermore yields conductors, which, for any furnace run, are sure to be uniform in size, composition, and electrical properties, and therefore adapted for use in series without previous sorting and weighing or other calibration.

What I claim as new and desire to secure by Letters Patent of the United States, is,

l. The method which consists in shaping a reducible compound of a refractory metal 105 into a thread, heating said thread in a furnace in the presence of a gaseous reducing agent to effect complete reduction of the compound, and firing the reduction product so obtained, under cover of said gaseous reducing agent, until said product is sintered to a condition of stable conductivity.

2.4 The method which consists in mixing a reducible compound of a refractory metal with a carbonaceous binding material, shaping said mixture into threads, simultaneously baking a plurality of said threads in a furnace containing hydrogen, to cause reduction of said compound, and firing the reduction product so obtained until it is sintered into a conductor of permanent conductivity.

3. The method of finishing tungsten filaments consisting essentially of material ob'- tained by reduction of tungsten trioxid with hydrogen, which consists in firing a plurality of said filaments in a furnace under protection pf hydrogen and a carbon absorbing means.

4. The method which consists in mixing tungsten trioXid with a binding material, shaping threads from the mixture so formed, simultaneously baking a plurality of said threads in hydrogen to eifect complete reduction' of the trioXid, and subsequently ring said filaments to about 1500 degrees G. in a reducing atmosphere free from carbon.

5. rlhe method which consists in mixing an oXid of tungsten With a carbonaceous binding material, shaping threads from the mixture so formed, simultaneously baking a plurality of said threads in a reducing atmosphere to effect complete reduction of the oxid, and subsequentlyiringsaid filaments under protection of a carbon absorbing means, continuing the heating until the tungsten is sintered'to a condition of stable conduetivity.

6. The method of finishing tungsten filaments, which consists in firing a plurality of said filaments in an open tube, and simultaneously protecting said filaments with hydrogen and rutile.

7. The method of finishing tungsten lilaments produced by reduction of an4 oxid of tungsten with carbon and hydrogen, which consists in iring a plurality of said filaments in a furnace under'proteetion of a carbon absorbing means, said firing being continued until the product is sintered to a condition of stable conductivity.

Inwitness whereof, I have hereunto set my hand this 23rd day of August, 1907.

CARL T. FULLER.

Witnesses:

HELEN ORFoRD, ABBA B. MARVIN, Jr. 

